1. Field of the Invention
The present invention relates to a method for producing a modified conjugated diene-based polymer and a method for producing a polymer composition using the polymer.
2. Background Art
In recent years, with an increase of interest in the environmental problems, improvement in fuel economy has strongly been required on automobiles, and a rubber composition to be used for automotive tires is also required to be superior in fuel economy. As a rubber composition for automotive tires, rubber compositions containing a conjugated diene-based polymer such as polybutadiene or a styrene-butadiene copolymer, and a reinforcing agent are used. The use of a silica reinforcing agent in place of carbon black, which has heretofore been used as a reinforcing agent, has been studied in order to improve performance se a rubber composition for tires.
Silica reinforcing agents are lower in affinity with conjugated diene-based polymers as compared with carbon black. Improvement in fuel economy has believed to require to enhance affinity between silica reinforcing agents and conjugated diene-based polymers. In order to enhance affinity between silica reinforcing agents and conjugated diene-based polymers, JP-A-10-7702, for example, proposes a method in which isoprene and butadiene are polymerized using n-butyllithium, n-butyllithium is then reacted with the resulting polymer to perform metallization of a vinyl group possessed by a side chain of the polymer, and thereafter chloropropyltriethoxysilane is reacted with the resultant metalized polymer to obtain a modified conjugated diene-based polymer.